Manhole closure



Dec. 31, 1935.- G, E, WOODS, JR y i 2,025,839

MANHOLE cLosURE. I Filed May i2, 1952 Patented Bec. 3l, 1935 MANHLE CILSURE George E. Woods, Jr.,

to Consolidated Gas New York, N. Y., assigner Company of New York,

New York, N. Y., a corporation of New York Application May l2, 1932, Serial No. 610,811

9 Claims.

This invention relates to manhole closures and the like and provides improvements therein.

When an explosion occurs in a manhole the cover, or covers where the manhole is provided with an inner and an outer cover, are usually fractured and parts or fragments projected with dangerous force for a considerable distance from the manhole. In manholes having an inner and an outer cover experience and experiments show that the fracturing, and consequent number of fragments, is considerably increased, many of the fragments being projected laterally in a low trajectory for a distance of several hundred feet. It has been found that these fragments are mostly parts of the inner cover, and the lateral projection thereof I attribute to the fact that the inner cover is either initially shattered, or is projected forcibly against the underside of the stronger cover and shattered. The outer cover, even though it is itself driven upwardly by the explosion, offers a resistance which forces the gases to spread laterally and carry with them the shattered parts of the inner cover.

The present invention provides a structure for closing manholes comprising either a single cover, or an inner and outer cover, and means whereby the projection of the outer cover under the force of an explosion is reliably restrained and the cover reliably retracted to a position which will cover or protect the manhole opening, without shattering and scattering of fractured parts, the inner cover, where one is used, being so constructed and arranged that it does not shatter, and is reliably retained within the cavity beneath the outer cover.

An embodiment of the invention is illustrated in the accompanying drawing, wherein: Figure 1 is a vertical sectional view through a .manhole provided with a closure according to the present invention, and showing the parts in normal closed position.

Fig. 2 is a similar view showing the closure parts in the maximum position to which they are driven by the force of an explosion.

Fig. 3 is a similar View showing the retracted position of the parts following an explosion.

Fig. 4 is a perspective view partly in vertical section, with the section at right angles to the sections shown in the preceding views.

Fig. 5 is a perspective view of a detail.

Fig. 6 is a view of a detail, showing in vertical section a portion of the inner cover with a packing interposed between the inner cover and the part of the hatch on which it seats.

Referring to said drawing, numeral I0 designates a manhole, which may be formed as usual of masonry il. with metal hatch M flush with the roadway and provided with a countersunk shoulder It.

The manhole illustrated is of the type having an 5 outer cover Eil and an inner cover 22 (sometimes called a pan) The invention herein set forth may nevertheless be embodied in manholes having an outer or single cover, and the novel features pertaining to the inner cover may be employed independently of the novel features pertaining to the outer cover, and vice versa.

The cover 2U is preferably heavy and strong and in closed position fits with its edge on the shoulder iii, substantially iiush with the roadway. l5

Numeral 25 designates yielding means for resisting the driving upward or projection of the cover 263 by the force of an explosion inside the manhole, and for retracting it to its closed or virtually closed position. 20

The means 25 preferably comprises a rod 26 attached to the center of the cover 20 and extending down into the manhole, and a spring 28 or equivalent restraining device. The spring 28 abuts or reacts against the lower part of the 25 rod 25, and for this purpose a washer 3l) confined by 'a nut or nuts 32 threaded on rod 26, may be provided. A part 3d firmly secured to a fixed part of the manhole it sustains the force or reaction of the upper end of spring 28 when the latter is compressed. The part 3i is preferably a bar extending diametrically across the manhole, having lugs at its ends adapted to fit into bayonet-joint sockets 3S, which are usually pro- Y vided on the inner sides The bar 34 is made strong to resist deformation by stresses thereon incident to restraining the cover 2@ following an explosion. 'I'he force and coaction of the spring 28, or other yielding means, is such that its elasticity is not exceeded by the force acting against it due to the explosion, so that the spring or other means does not jam and produce ashock on the cover which, added to the strain already thereon, would have a strong tendency to cause the cover to break. The spring is long and the modulus of elasticity of the spring such that a small force will cause a considerable compression. The result is that the outer cover offers little initial resistance other than its own inertia to being raised. As soon as it has been lifted a vent for the gases is at once provided without either rupturing shock or impact to any part of the device.

The rod 26 is preferably connected to the center of the cover 20, and guided in a central openof manhole hatches I4. 35

ing 38 in the restraining bar 34. The strain on the cover 20 produced by the pull of the rod 26 against the force of an explosion is thereby nearly symmetrically distributed in the cover and liability to cracking very much diminished. Also by this arrangement it is possible to utilize the type of outer cover now generally in use without any change. In those cases where Ventilating holes are not provided the existing covers can be used by merely drilling one hole in the center of them. Moreover, the pull of the cover on rod 26 is thereby made to act substantially in line with the axis of the manhole, and liability of the rod 26 to being bent and causing interference with the action of the spring to retract the cover to a position covering or virtually covering the manhole, avoided. Furthermore by this arrangement the yielding means can be utilized without attaching anything permanently to the manhole vault or altering it in any way, as the central unattached position of the rod is out of the way of ladders used for descending and is removed from the opening together with and as an integral part of the device.

The cover 2 may be detachably connected to the rod 25 by a cap-screw 4D having threaded connection with a nut or sleeve 42 on the upper end of rod 25. The cap-screw 40 may be provided with Spanner-holes 44 (Fig. ll) for turning.

The cover 22 is of a form to resist shattering under the force of an explosion. For this purpose thecover 22 is preferably made of a sheet of ductile metal, such as ductile steel, capable of readily bending under the force of an explosion under the covers. Moreover, the cover 22 of ductile metal is preferably provided with means for directing the bending of the cover under the force of an explosion so that when the cover is fastened portions thereof may turn up in the manner of flaps, as indicated at 50. Areinforcement or bar 55 across the top of cover 22, may be provided for directing the bending of cover 22, and such means are preferably arranged to extend diametrically in line with bar 34 when the latter is also employed. In a closure including both an inner cover 22 and an outer cover 25, the restraining construction heretofore described is preferably employed, and the bar V34 may be provided -with means, as bolts 55, adapted to bear on the inner cover 22 and fasten and hold it against the shoulders 58 on the hatch I4. In the absence of other means, the underside of the bar 3 extending diametrically across the manhole and across the cover 22 would act to direct the bending. The rod 25 would extend through the cover 22, and the upper end of spring 28 would bear on the underside of said cover 22, the bar 34 ultimately sustaining the force exerted through spring 28. When only an outer cover is used the upper end of the yielding means will react against the underside of the retaining bar 34.

In many instances the inner covers of the manhole closures are arranged to seal the opening through the manhole for the purpose of making the space below the manhole watertight, etc. The cover 22 so arranged is illustrated in Fig. 6; a packing is interposed between the shoulder 58 of the hatch I4 and the edge of the cover 22, and the bolts 55 may be screwed down onto the cover 22 so as to compress the packing against shoulder 58 and provide a tight joint to thereby seal the opening. Preferably the cover 22 is provided with a channel or groove 62 in its peripheral portion to receive or contain the pack-s ing 65 in the form of a washer or gasket.

The cover 20 may be of the ventilated type, or may be imperforate. In Fig. 4 the cover 20 is shown as provided with openings 66; in the 5 other gures the cover 20 is shown without openings.

The inner cover 22 may also be of the ventilated type, or may be imperforate. In Fig. 4 the inner cover 22 is shown as provided with 10 openings 58, and in the other figures it is shown without openings.

Operation When an explosion in a manhole occurs, the force will bend the inner cover, the bending being directed by the reinforcing web or bar 55 or other means, and the cover-parts or flaps 50 will open allowing gas to pass and avoiding shattering of the cover 22, especially when made of ductile metal. rIhe fastening means (bar 34 and bolts 20 56 in the illustrated embodiment) will hold the cover 22 against being blown out of the manhole. The force of the explosion against the underside of cover 25 vwill lift itagainst the reaction of 2.5 the spring 28 or other restraining means. As soon as the outer cover 20) has opened, the initial force of the spring being slight, practically the only resistance that the outer cover will offer is its own inertia which is small enough to prevent shattering from the initial shock and will permit it to rise. As soon as it has been raised oi its seat a vent is at once provided which relieves the explosive force more and more as the opening widens until the reacting force due to, the spring which is becoming greater as the opening increases is able to overcome the explosive force which diminishes as the vent becomes larger. The outer cover will therefore come to rest without jar or shock before the spring has been completely compressed and, when the force of 40 lthe explosion has been spent, will be retracted to its original position. If the upwardly bent flaps 55 of the inner cover 22 project so high as to strike the underside of cover 20, the manhole will be virtually covered, as illustrated in Fig. 3, 45 so as to protect the opening against anyone falling in. Moreover the dangers consequent upon shattering and scattering of the shattered parts are avoided. No other consequence than deformation of the inner cover, which is readily re- 50 placeable, need follow a manhole explosion when a manhole is provided with a closure according to the present invention.

The invention may receive other embodiments. 6 than that herein specically illustrated and described.

What is claimed is:

1. A manhole closure consisting of an inner and an'outer cover, the outer cover resting on itsoo seat at the outer surface of the manhole under normal conditions and being capable of rising under explosive forces, the inner cover being of flexible material and having means for retaining it substantially below the upper surface of the manhole against bodily projection under explosive forces.

2. A manhole closure consisting of an inner and an outer cover, the outer cover resting on its seat at the outer surface of the manhole under normalr 70 conditions and having means for yieldably restraining its upward projection under explosive forces, the inner cover being of flexible material to permit bending under the inuence of explosive forces and means for retaining the inner -cover'l75 substantially below the upper surface of the manhole against bodily projection under such explosive forces.

3. A combination according to claim 2, Wherein said exible inner cover is provided with means for guiding the bending thereof under the action of explosive forces.

4. A combination according to claim 2, wherein proJection of the outer cover is a rod attached to 5. A combination according to claim 2, wherein inner cover across the manhole and engaging xed parts in the manhole. 6. A combination according to claim 2, wherein said means for retaining said inner cover in the manhole is a retaining-bar extending above the 2B means for yieldably restraining the upward pro- 30 rod and said retaining-bar, which latter acts as 7. A combination according to claim 2, wherein said means for retaining said inner cover in the l5 manhole and engaging fixed parts in the manhole, and wherein said flexible inner vr has a diametral reinforcement arranged to be alined with said retaining-bar and to guide the bending of the flexible inner cover under the action of explosive forces, and means on said retaining- 5 bar for bearing on said diametral reinforcement to normally press said inner cover against its seat. 8. A closure for a manhole comprising an outer against which said spring acts.

9. A closure for a manhole comprising an outer tion of said cover by the force of an explosion, a yieldable inner cover, a retaining-bar extending GEORGE E. WOODS, JR. 86 

